The wavelength of light in the visible region is about 390 nm for violet colour, about 550 nm (average wavelength ) for yellow - green colour and about 760 nm for red colour .
From which of the photosensitive materials with work functions listed in table and using the results of (i) , (ii) and (iii) of (a) can you build a photoelectric device that operates with visible light ?

Explanation

For a photoelectric device to operate, we require incident light energy E to be equal to or greater than the work function `phi_(0)` of the material . Thus , the photoelectric device material Na ( with `phi_(0) = 2.75` eV) , K ( with `phi_(0) = 2.30` eV) and Cs ( with `phi_(0) = 2.14` eV) . It will also operate with yellow - green light (with E = 2.26 eV) for Cs (with `phi_(0) = 2.14` eV) only . However, it will not operate with red light ( with E = 1.64 eV) for any of these photosensitive materials .